This invention relates to improvements in electrographic development apparatus wherein developer material is mixed and triboelectrically charged in a sump before delivery to a magnetic brush for development of an electrostatic image. More specifically, the invention relates to an improved development apparatus having a ribbon blender for mixing and tribocharging developer material in a sump.
Electrographic development apparatus are well known in the art. Such apparatus may include a housing in which developer material is located and a magnetic brush that receives such material from the housing and transports it to a position where part of such material can be transferred to an electrostatic image formed on an insulating surface to thereby develop the image. The developer material may comprise a mixture of carrier particles and smaller toner particles. Some of the toner particles are transferred from the mixture to the electrostatic image during development of the image. Thus there is a need to replenish toner particles in used developer material in the housing. In order to replenish toner particles in used developer material, the used developer material can be delivered from the housing to an end sump along with the addition of fresh toner particles. The materials in the end sump are then mixed and agitated in order to thoroughly mix the fresh toner particles with the used developer material and to effect triboelectric charging of the materials. The resulting toner-replenished developer material is then transported from the end sump to the housing by means of augers or other apparatus so that the development material is again available for transfer of toner to a magnetic brush for development of an electrostatic image. An apparatus of this general type is disclosed in commonly assigned U.S. Pat. No. 4,101,211, issued July 18, 1978 in the name of Walter Kayson and entitled MAGNETIC CURTAIN SEAL FOR DEVELOPMENT APPARATUS. Such development apparatus requires relatively high circulation rates in order to transport toner replenished development material from the end sump along the entire length of the housing of the development station. Such high circulation rates increase power requirements for the development apparatus and decrease the developer life.
Recently a new developer material has been developed wherein the carrier particles comprise permanent magnets. The particles in such a material have a tendency to cling to each other to form clumps and, in general, in the absence of an external field, such materials have a tendency to behave somewhat like wet sand due to the magnetic attraction exerted between the particles. Such a material creates special problems in mixing developer material, circulating the material axially along a development station, agitating and shearing the developer to promote tribocharging and then feeding the developer to a magnetic brush. A material of this type is disclosed in the commonly assigned copending U.S. patent application Ser. No. 548,807, filed on Nov. 4, 1983 in the names of E. T. Miskinis et al, and entitled TWO COMPONENT, DRY ELECTROGRAPHIC DEVELOPER COMPOSITIONS CONTAINING HARD MAGNETIC CARRIER PARTICLES AND METHODS FOR USING THE SAME, now U.S. Pat. No. 4,546,060, issued Oct. 8, 1985.